When multicolor information is to be imaged or written, a final compound color is obtained, in general, by superimposing print separations. Each print separation has a different basic color, and the color separation prints are coordinated with and aligned relative to each other. In general, a plurality of dots or patches, each of different basic colors, are printed in a same locality so as to be aligned with or superimposed on each other. Such superposition of print separations gives the impression of a full color image having colors that may be different from the basic colors.
Normally three or four separations are used, each with a basic (process) color, (or optionally, black) in order to obtain a final compound color. In some cases additional color separations are also used. The final compound image is obtained by finely adjusting, through alignment of the system, the position of each separation, to accurately overlay the separation prints. The alignment process and the alignment itself are called registration.
When the separations are printed slightly out of registration, the appearance of an image is slightly impaired. However, if the separations are more than slightly out of registration, the effect will be disturbing to an observer. In particular, the individual edges of objects formed by each one of the separations will separate and the quality of the final multicolor image will be greatly impaired.
WO 00/43206 to Indigo, N. V., the disclosure of which is herein incorporated by reference, describes an apparatus and method for correcting print separation registration in a printing apparatus or photocopier.